An image forming device comprising, for example, a reflection-type polarizing filter and a retroreflective prism, and urging a display image to be reflected by the polarizing filter, reflected by the retroreflective prism, and transmitted through the polarizing filter to form the image has been proposed. Incidentally, if a retroreflector array corresponding to a reflective surface of a retroreflective prism has a discontinuous area, the light incident on the discontinuous area may not be retroreflected and, consequently, the display image may become discontinuous.